1. Field of the Invention
The present invention relates to a beam irradiation device for irradiating laser light onto a targeted area, and more particularly to a beam irradiation device to be loaded in a so-called laser radar system for detecting presence or absence of an obstacle or a distance to the obstacle in a targeted area, based on reflected light obtained by irradiating laser light onto the targeted area.
2. Disclosure of Related Art
In recent years, a laser radar system for irradiating laser light in a forward direction with respect to a driving direction to detect presence or absence of an obstacle or a distance to the obstacle in a targeted area, based on a state of reflected light of the laser light, has been loaded in a family automobile or the like to enhance security in driving. Generally, the laser radar system is so configured as to scan a targeted area with laser light to detect presence or absence of an obstacle at each of scanning positions, based on presence or absence of reflected light at each of the scanning positions. The laser radar system is also configured to detect a distance to the obstacle at each of the scanning positions, based on a required time from an irradiation timing of laser light to a light receiving timing of reflected light at each of the scanning positions.
Heretofore, there has been known scan mechanisms using laser light, such as a scan mechanism incorporated with a polygon mirror, and a scan mechanism incorporated with a scanning lens to be driven two-dimensionally. In addition, there has also been known a scan mechanism incorporated with a pivotal mirror for causing laser light to scan a scanning area.
In the laser radar system incorporated with the scan mechanism, a drive-control operation of a laser light source is performed based on a time elapsed from start of a scanning operation. For instance, laser light is pulse-emitted toward a targeted area at every predetermined time interval from start of a scanning operation.
It is necessary to increase the amount of computation and the number of times of computation operations to be performed by a circuit for controlling the scan mechanism to properly scan a targeted area with laser light. The processing load of a control circuit can be reduced by roughly controlling the scan mechanism. The control, however, fails to properly scan the targeted area with laser light. In this arrangement, if laser light is emitted based on a lapse of time from start of a scanning operation in the above-described manner, the irradiated position of pulse-emitted laser light may be displaced from an intended position, which may deteriorate irradiation precision of laser light with respect to the targeted area.